The present invention relates to an electrode of secondary batteries and a method for the preparation thereof. More particularly, the invention relates to a high-performance electrode of alkali storage batteries such as nickel metal hydride batteries as well as to a method for the preparation thereof.
It is a remarkable trend of electronic technologies in recent years that various kinds of very compact and portable electronic instruments, such as portable telephones and the like, are acquiring wide prevalence. Since these instruments are operated with batteries as the power source, the utilizability thereof largely depends on the performance of the batteries, in most cases, in the form of a cylindrical sealed secondary battery which is desired to have a high energy capacity and is of low costs. Alkali storage batteries are used, as the major current, as the secondary battery in the portable instruments. As the material of the electrodes in these secondary batteries, spongy or porous metal sheets are high-lighted in recent years as the substrate to be impregnated with an active material of the electrode as is disclosed in Japanese Patent Kokai 57-52479, 61-42377, 62-54235 and 63-81767.
The above mentioned spongy metal sheet is prepared from a base body of a foamed resin sheet having a three-dimensional network structure which is first subjected to a plating treatment of a metal such as nickel followed by direct impregnation of the skeletal structure with an active material of the electrode and shaping the body into the form of a battery electrode.
The above described prior art method for the preparation of a battery electrode has a problem as mentioned below. As is schematically illustrated in FIG. 1 of the accompanying drawing, namely, it is sometimes the case that the skeleton 1 of the base body of a foamed resin forming open pores 2 has spiky fragments 3A or dendritic protrusions 3B formed on the surface of the skeleton 1 of the foamed resin and is partly covered with a thin membrane 3C bridging the skeleton to cause sealing of the pores so that the spongy metal sheet may suffer from a decrease in the smoothness of impregnating work of the open pores in the skeleton with a pasty active material and/or catalyst of the battery electrode. Accordingly, the amount of impregnation of the skeletal structure with an active material or catalyst is necessarily decreased. When the electrode sheet after impregnation with the active material and catalyst is overlaid with an electrode separator sheet and wound together into the form of a cylindrical roll, in addition, the needlelike or spiky fragments 3A and/or dendritic protrusions 3B in the electrode sheet sometimes pierce the separator sheet to cause shortcircuiting between the positive and negative electrodes of the battery so that the life of the battery is greatly decreased.